The advisers accept that policy changes will be needed to make the transition to using cleaner fuels.

"Most model results indicate that known technological options could achieve a broad range of atmospheric CO2 stabilisation levels...over the next 100 years or more, but implementation would require associated socio-economic and institutional changes," they said.

G8 pledge

In the short term, "at least up to 2020", energy supply would remain dominated by fossil fuels which are relatively cheap and abundant, the report said. But natural gas could be used more and play an important role in emission reduction, it added.

The Accra report was released the day after environment ministers from the world's leading industrialised nations pledged in Trieste, Italy, to finalise a 1997 pact on cutting pollution that none of them has yet ratified.

Monday's report is the third of four studies by the IPCC.

The first, released in Shanghai in January, said the world was warming faster than previously predicted, and found increasingly strong evidence for human activities as a cause.

The second, released in Geneva in February, found that if warming through greenhouse gases like carbon dioxide was not slowed and then turned around in coming decades the planet could see huge floods, spreading disease and social chaos.

The fourth, due in September, will summarise all three.

The stance taken in Monday's document on the likely impacts of climate change shows a greater degree of certainty than was evident in the draft leaked to BBC News Online last month.

Some of the more equivocal statements have been removed. The draft seen by News Online said policymakers should be ready for "possible revision of the scientific insights into the risks of climate change". These words have gone.

The draft also talked about "appropriate hedging" until there was agreement on the level at which greenhouse gas emissions should be stabilised. Monday's document now talks about a "step-by-step" approach to stabilisation that "balances the risks of either insufficient or excessive action".

This toughening will disappoint those who thought that at least one section of the IPCC might be more willing to engage some of the uncertainties that dog climate science. There are scientists who feel the IPCC has overlooked much recent research which throws into doubt some of the foundations on which the global warming hypothesis is built.

Just this week, the Bulletin of the American Meteorological Society put out a study that showed how cloud changes in the Pacific could limit future rises in temperature.